WC138 SeptOct 2024 - Flipbook - Page 21
with collar joints, which are more rigid, are more susceptible to
breaks due to soil movement and changes in moisture content.
Additionally, cast iron pipes lined with cured-in-place (CIP) or
cement mortar (CM) linings are more likely to fail during this
period, likely due to external corrosion exacerbated by increased
rainfall and higher soil moisture levels. These insights into trends
can support better maintenance and rehabilitation planning, reducing costly reactive work. They can also inform future cost-efficient design, such as the selection of pipe materials, joint types,
and lining types. Moreover, better locating pipes and educating
contractors could help avoid accidental damage during the busy
summer construction season in Canada.
Failure causes and types
Important trends were also observed over the pipe’s life cycle. In
the first 20 years, accidents and joint or fitting failures are most
common. These failures are often due to installation errors, and
the study was able to pinpoint that universal joints are particularly prone to failure at this age. Universal joints use bolts to fasten
pipes with a taper seat and are generally used with cast iron pipes.
Between 20 and 40 years, pipes are more likely to experience
failures due to differential settlement and the development of
holes from corrosion. As pipes age beyond 40 years, material deterioration becomes more prevalent, with circumferential breaks
becoming the dominant failure mode between 40 and 60 years.
Understanding these trends can help utilities improve installation
practices and prioritize inspections, focusing on different potential locations of weaknesses throughout the pipe’s life cycle.
Soil type
At the installation stage, it is also important to consider soil type
and its role in pipe stability. Uneven bedding or the protrusion
of rocks can lead to early failures. The study found that pipes
installed in clay soil are more likely to suffer from improper
bedding and greater soil movement, leading to a higher incidence
of circumferential breaks. Sandy soils contribute to differential
settlement and are prone to accidents, increasing the likelihood
of failures at joints and fittings. Furthermore, pipes laid in gravel
and rock soils are more susceptible to breaks and holes due to the
coarser nature of these materials.
Lessons learned
Cleaning and joining the data from 13 utilities was a complex
task. Consistent categories were defined for every variable, which
sometimes meant transforming comments recorded on site into
standardized categories. The development of standard definitions
and categories for failure cause and type is also recommended for
utilities to reduce subjectivity and variability in data recording.
The researchers also faced inconsistencies in historical data. In
many cases, pipe identifiers were reused in the datasets after the
pipes were replaced, causing historical data to be lost. It is recom-
WAT E R C A N A D A . N E T
mended that utilities always assign new identifiers to new pipes to
ensure this data can be used in the future.
Practical implications
The findings of this comprehensive study can lead to practical
strategies. Improved joint installation practices can reduce early
watermain failures, while better control of bedding, backfilling,
and compaction will minimize soil movement and related failures.
Preventative maintenance targeting break-prone pipes with collar
joints and coal tar lining can reduce costly reactive repairs. More
accurate pipe location data and better contractor education could
help avoid accidental breaks, particularly during busy construction
seasons. Additionally, understanding seasonal trends helps utilities
better plan maintenance and rehabilitation work throughout the
year, optimizing resource allocation and reducing disruptions.
These insights highlight a systematic approach to managing watermain failures. By improving predictions of breaks and combining
this with regular inspections and knowledge of pipe criticality,
utilities can achieve more reliable water infrastructure.
The full study can be accessed here.
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